This invention relates to exhaust vent systems for clothes dryers.
Dryer exhaust conduits conduct substantial quantities of heated air and lint from the dryer to an external location Because of the amount of thermal energy involved in the vented air and in the dryer itself, dryer hose installation should be carefully made by a skilled serviceman. A kinked or crushed conduit could create highly undesirable air flow restriction causing reduced velocity resulting in lint buildup in locations of reduced velocity This lint buildup constitutes combustible material in the event of a fire in the dryer.
Underwriters Laboratory, being well aware of these problems, will not allow the UL listing for any dryer unless the manufacturer uses all metal connections and conduit in the vent system in order to contain any fire within the dryer and vent system. Unfortunately, the persons that frequently install dryers are delivery people hired by retailers to drive truck and unload equipment. They too often are without the metal working skills required to make an effective dryer exhaust hookup of metal components. Therefore, such delivery people largely refuse and/or are simply unable to use metal duct and connectors as required by UL, because such are too complex for their skill level. Yet, they are commonly required by their employers to install the dryer vent system. Consequently, they use whatever materials are easy to manipulate, usually accordion type vinyl duct, and connect them any way they can. The results are far from ideal. Vinyl duct tends to collect lint along its length if kinked. Moreover, vinyl duct is not noncombustible Hence, if a fire should occur in the dryer, it cannot be contained by the vent hose. The Consumer Products Safety Commission reported that in 1987, 13,900 clothes dryer fires occurred in the U.S.
Another difficulty in installing clothes dryer vent systems is the limited space available to do the work. Dryers typically are fitted into a space just wide enough to receive them, i.e., straddled by walls, a washing machine, a cabinet, or shelving. Typically, therefore, it is practically impossible to make the vent connection after the dryer is against the wall. By making the connection when the dryer is still spaced several feet from the wall too often results in not being able to get the dryer close to the wall after the installation or, if it is pushed close to the wall, the hose sometimes gets crushed, kinked and/or flattened, resulting in poor air flow.
Dryer manufacturers are therefore concerned about poor dryer performance from an improper installation, as well as about potential legal liability in the event of overheating caused by a poor vent arrangement, and failure of the dryer safety controls to shut down the dryer before ignition temperature is achieved. The manufacturer can supply metal connector and duct material to the retailer with the dryer and stipulate that only metal duct components are to be used, but when the delivery person takes the dryer from the retailer to the purchaser, the manufacturer has no effective way of forcing him to install the dryer conduit using metal ducts and connectors.
The problem has been further compounded in recent years due to a tendency to place dryers in small closets. Typically such a closet will have a maximum of about 33 inches clearance. There is little or no room to make the vent hookup unless the dryer is outside of the closet at the time. Then, when it is pushed into the closet, several things, some bad, can happen to the dryer hose and connection.
Hence, in spite of the initial efficiency of the dryer as manufactured, and the theoretical connection to a freely flowing exhaust, in practice dryers may well not achieve this type of efficiency, and moreover the dryer and/or the vent duct are susceptible to overheating because of inadequate air flow through the vent system, failure of safety circuits, and collection of combustible lint.